48, XXYY syndrome is a sex chromosome variation that affects one in every 17,000 boys who are born.
48, XXYY is one of several types of sex chromosome variations, including those that are considered as variants of Klinefelter Syndrome, 47 xxy and xxxy, xxxxy, xy/xxy and another syndrome called xyy, all of which affect males. Similar female syndromes include Turner Syndrome (xo) and several variations with added x's. There are important differences, between boys with 47,XXY and 48,XXYY and some authors have questioned whether 48,XXYY males should be included under the umbrella of Klinefelter Syndrome.
48 XXYY is not an Intersex condition or indication. Please read our notice on XXYY and Intersex Conditions.
 The incidence of 48,XXYY syndrome was originally estimated at 1/50,000 (Sorensen et al., 1978), but a recent report found the 48,XXYY karyotype in 1/17,000 males in a newborn screening (Nielsen et al., 1991).
 Grarnmatico et al., 1990 Males with xxyy have two x and two y sex chromosomes, instead of one each. XXYY is sometimes considered a variant of another syndrome called Klinefelter Syndrome, or 47 xxy. There are other types of sex chromosome anomalies such as xyy, xxxy, xxxxy, and variations in girls such as xo (Turner Syndrome), xxx, xxxx. and xxxxx.
Although there have been limited studies and research on xxyy, the fact that xxyy boys have many similar features is often not mentioned.
New research on XXYY Syndrome is currently under way. Visit our Research page for more information.
The XXYY Project seeks your support for more medical research, programs, treatment and services.
What are the characteristics &
causes of XXYY and how is it diagnosed?
XXYY is often mistaken for other syndromes. The most common symptoms and characteristics that would be noticeable by parents, teachers, medical professionals and other treatment providers are:
Tall, considering family history
Behavior outbursts & mood swings
Autism, autism spectrum, PDD-NOS
Clinodactyly (Curved-in pinky fingers)
Low muscle tone
Delayed sexual development
Low or no testosterone
(Not all boys with xxyy experience all of these symptoms)
Cause and Rate of Occurance
The cause of XXYY syndrome is still not completely understood. Since extensive studies have not been conducted on the cause of XXYY, there is currently very little information about whether or not there are environmental or other factors. However, there is no evidence that parents of one XXYY child are more likely to have other children with sex chromosomal variations. Sex chromosomal variations in general are actually quite common. The occurance of XXYY is 1 in 17,000 live male births. Klinefelter Syndrome, XXY, is 1 in 500.
Diagnosing xxyy requires a genetic test called a karyotype. The test is done by drawing blood and an analysis is done on the cells of the blood to determine the boy's chromosomal make-up. In some instances, a boy can have some normal xy cells and some xxyy cells. This test is the only way to know for certain that a boy has xxyy.